FHLB Advances and Other Borrowings - Schedule of Advances, Related Party Notes (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Sep. 30, 2016
Debt Instrument [Line Items]
Total	$ 711,000	$ 871,000
Fair value adjustment	29	37
Total FHLB advances and other borrowings	711,029	871,037
Notes payable to banks
Debt Instrument [Line Items]
Federal Home Loan Bank (FHLB) notes payable and fed funds advance	$ 636,000	$ 640,000
Notes payable to banks | Minimum
Debt Instrument [Line Items]
Stated interest rate (as a percent)	0.66%	0.66%
Notes payable to banks | Maximum
Debt Instrument [Line Items]
Stated interest rate (as a percent)	3.66%	3.66%
Federal Home Loan Bank fed funds advance
Debt Instrument [Line Items]
Interest rate (as a percent)	0.81%	0.81%
Federal Home Loan Bank (FHLB) notes payable and fed funds advance	$ 75,000	$ 231,000